Current source inverter and operation method thereof

ABSTRACT

A current source inverter includes a controller, an input unit, a buffer unit, a modulating unit, and a commutator. The controller generates a switch control signal, an inverse switch control signal, a first pulse width modulation control signal, and a second pulse width modulation control signal. The input unit stores and transmits input power of a direct current power supply according to the first pulse width modulation control signal. The buffer unit is coupled to the input unit for receiving and transmitting the input power. The modulating unit generates and outputs a full-wave rectified sinusoidal current according to the second pulse width modulation control signal and the input power. The commutator converts the full-wave rectified sinusoidal current into an alternating current according to the switch control signal and the inverse switch control signal and outputs the alternating current to a load or a utility line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a current source inverter and anoperation method thereof, and particularly to a current source inverterand an operation method thereof that have advantages of a simple controlmethod, less power conversion times, higher power conversion efficiency,and so on.

2. Description of the Prior Art

Generally speaking, an inverter can convert input power of a directcurrent power supply into alternating current power, and output thealternating current power to a load or a city main. If a voltage and acurrent of the load or the city main coupled to the inverter are inphase, a frequency of the alternating current power is two times to afrequency of the voltage and the current of the load or the city main,and the alternating current power can inversely influence the directcurrent power supply and generate low frequency current ripples on thedirect current power supply. If the direct current power supply is arenewable energy (e.g. solar energy or wind energy), the direct currentpower supply with the low frequency current ripples may reduceefficiency of a maximum power output function of the renewable energy.Therefore, how to design an inverter that can reduce influence on thedirect current power supply caused by the alternating current power ofthe load or the city main becomes an important issue for an inverterdesigner.

SUMMARY OF THE INVENTION

An embodiment provides a current source inverter. The current sourceinverter includes a controller, an input unit, a buffer unit, amodulating unit, and a commutator. The controller is used for generatinga switch control signal, an inverse switch control signal, a first pulsewidth modulation control signal, and a second pulse width modulationcontrol signal. The input unit is coupled to a direct current powersupply, and used for storing and transmitting input power of the directcurrent power supply according to the first pulse width modulationcontrol signal. The buffer unit is coupled to the input unit forreceiving and transmitting the input power. The modulating unit iscoupled to the buffer unit for receiving the input power according tothe second pulse width modulation control signal, and generating andoutputting a full-wave rectified sinusoidal current according to theinput power. The commutator is coupled to the modulating unit forconverting the full-wave rectified sinusoidal current into analternating current according to the switch control signal and theinverse switch control signal, and outputting the alternating current toa load, wherein a frequency of the switch control signal and a frequencyof the inverse switch control signal are equal to a frequency of theload. The controller controls an enabling time of the second pulse widthmodulation control signal according to the sinusoidal current, and anenabling time of the first pulse width modulation control signal isgreater than the enabling time of the second pulse width modulationcontrol signal.

Another embodiment provides an operation method of a current sourceinverter, wherein the current source inverter includes an input unit, abuffer unit, a modulating unit, a controller, and a commutator. Theoperation method includes the controller generating a first pulse widthmodulation control signal and a second pulse width modulation controlsignal; and the input unit executing a first corresponding operationaccording to the first pulse width modulation control signal, and themodulating unit executing a second corresponding operation and thebuffer unit executing a third corresponding operation according to thesecond pulse width modulation control signal.

The present invention provides a current source inverter and anoperation method thereof. The current source inverter and the operationmethod utilize an input unit to execute a first corresponding operationaccording to a first pulse width modulation control signal, a modulatingunit to execute a second corresponding operation according to a secondpulse width modulation control signal, and a buffer unit to execute athird corresponding operation according to the second pulse widthmodulation control signal. Therefore, compared to the prior art, thepresent invention has advantages as follows: first, because a controllercan control turning-on and turning-off of a first switch and a secondswitch through the first pulse width modulation control signal and thesecond pulse width modulation control signal, low frequency currentripples inversely generated by sinusoidal power outputted by themodulating unit modulating unit can be absorbed by the buffer unit,resulting in low frequency current ripple components of input powerbeing decreased, to increase power conversion efficiency of the currentsource inverter; second, when the current source inverter (isolationtype) operates, because a voltage drop of a first capacitor is connectedto a voltage drop of a second capacitor in series, the voltage drop ofthe second capacitor does not need to be higher than a voltage drop of aload, resulting in the second switch easily transmitting power to theload and not enduring stress corresponding to longer turning-on time,and operation range of a direct current power supply being also verylarge; third, because a first inductor and a second inductor of thecurrent source inverter operate in a continuous current mode (CCM),current stress on the first switch and the second switch is not verylarge; and fourth, second switches of some current source invertersprovided by the present invention can be still turned on throughparasitic diodes thereof during a mode III, so the second switches ofthe some current source inverters provided by the present invention havea zero voltage switching characteristic when the second switches of thesome current source inverters provided by the present invention areswitched from the mode III to a mode I, resulting in switching loss ofthe second switches of the some current source inverters provided by thepresent invention being decreased.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a current source inverter according toan embodiment.

FIG. 2 is a relationship diagram illustrating the first pulse widthmodulation control signal, the second pulse width modulation controlsignal, a first inductor current flowing through the first inductor, andthe second inductor sinusoidal current flowing through the secondinductor.

FIG. 3 is a diagram illustrating the current source inverter in a modeI.

FIG. 4 is a diagram illustrating the current source inverter in a modeII.

FIG. 5 is a diagram illustrating the current source inverter in a modeIII.

FIG. 6 is a diagram illustrating a current source inverter according toanother embodiment.

FIG. 7 is a diagram illustrating the current source inverter in a modeI.

FIG. 8 is a diagram illustrating the current source inverter in a modeII.

FIG. 9 is a diagram illustrating the current source inverter in a modeIII.

FIG. 10 is a diagram illustrating a current source inverter according toanother embodiment.

FIG. 11 is a diagram illustrating the current source inverter in a modeI.

FIG. 12 is a diagram illustrating the current source inverter in a modeII.

FIG. 13 is a diagram illustrating the current source inverter in a modeIII.

FIG. 14 is a diagram illustrating a current source inverter according toanother embodiment.

FIG. 15 is a diagram illustrating the current source inverter in a modeI.

FIG. 16 is a diagram illustrating the current source inverter in a modeII.

FIG. 17 is a diagram illustrating the current source inverter in a modeIII.

FIG. 18 is a flowchart illustrating an operation method of a currentsource inverter according to another embodiment.

FIG. 19 is a flowchart illustrating an operation method of a currentsource inverter according to another embodiment.

FIG. 20 is a flowchart illustrating an operation method of a currentsource inverter according to another embodiment.

FIG. 21 is a flowchart illustrating an operation method of a currentsource inverter according to another embodiment.

DETAILED DESCRIPTION

Please refer to FIG. 1. FIG. 1 is a diagram illustrating a currentsource inverter 100 (isolation type) according to an embodiment. Thecurrent source inverter 100 includes a controller 102, an input unit104, a buffer unit 105, a modulating unit 106, and a commutator 108. Thecontroller 102 is used for generating a switch control signal SCS, aninverse switch control signal SCS, a first pulse width modulationcontrol signal FPWM, and a second pulse width modulation control signalSPWM. The input unit 104 is coupled to a direct current power supply110, and used for storing and transmitting input power PDC of the directcurrent power supply 110 according to the first pulse width modulationcontrol signal FPWM, wherein the input power PDC is equal to a productof a direct current IDC and a direct current voltage VDC provided by thedirect current power supply 110. In addition, the direct current powersupply 110 is a solar panel, and the input unit 104 has a maximum powerpoint tracking (MPPT) function, wherein the direct current IDCcorresponds to the maximum power point tracking function of the inputunit 104. But, the present invention is not limited to the directcurrent power supply 110 being a solar panel, that is, the directcurrent power supply 110 can also be any stable direct current powersupply. The buffer unit 105 is coupled to the input unit 104 forreceiving and transmitting the input power PDC. The modulating unit 106is coupled to the buffer unit 105 for receiving the input power PDCaccording to the second pulse width modulation control signal SPWM, andgenerating and outputting a full-wave rectified second inductorsinusoidal current IL according to the input power PDC. The commutator108 is coupled to the modulating unit 106 for converting the full-waverectified second inductor sinusoidal current IL into an alternatingcurrent IAC according to the switch control signal SCS and the inverseswitch control signal SCS, and outputting the alternating current IAC toa load 112 (e.g. an alternating current load), wherein a frequency ofthe switch control signal SCS and a frequency of the inverse switchcontrol signal SCS are equal to a frequency of the load 112. But, thepresent invention is not limited to the current source inverter 100outputting the alternating current IAC to the alternating current load,that is, the current source inverter 100 can also output the alternatingcurrent IAC to a city main.

As shown in FIG. 1, the input unit 104 includes a first inductor 1042and a first switch 1044. The first inductor 1042 has a first terminalcoupled to a first terminal of the direct current power supply 110, anda second terminal. The first switch 1044 has a first terminal coupled tothe second terminal of the first inductor 1042, a second terminal forreceiving the first pulse width modulation control signal FPWM, and athird terminal coupled to first ground GND1, wherein the first switch1044 is turned on (ON) and turned off (OFF) according to the first pulsewidth modulation control signal FPWM.

As shown in FIG. 1, the buffer unit 105 includes a transformer 1052, afirst capacitor 1054, a magnetizing inductor 1056, and a secondcapacitor 1058. The first capacitor 1054 has a first terminal coupled tothe second terminal of the first inductor 1042, and a second terminalcoupled to the transformer 1052. The magnetizing inductor 1056 has afirst terminal coupled to the second terminal of the first capacitor1054 and the transformer 1052, and a second terminal coupled to thefirst ground GND1 and the transformer 1052. The second capacitor 1058has a first terminal coupled to the transformer 1052, and a secondterminal coupled to the modulating unit 106.

As shown in FIG. 1, the modulating unit 106 includes a second switch1062, a first diode 1064, a second inductor 1066, and a third capacitor1068, wherein the second switch 1062 has a parasitic diode 10622. But,in another embodiment of the present invention, the parasitic diode10622 can be replaced with a physical diode. The second switch 1062 hasa first terminal coupled to the second terminal of the second capacitor1058, a second terminal for receiving the second pulse width modulationcontrol signal SPWM, and a third terminal, wherein the second switch1062 is turned on and turned off according to the second pulse widthmodulation control signal SPWM. The first diode 1064 has a firstterminal coupled to second ground GND2, and a second terminal coupled tothe third terminal of the second switch 1062. The second inductor 1066has a first terminal coupled to the second terminal of the first diode1064, and a second terminal. The third capacitor 1068 has a firstterminal coupled to the second terminal of the second inductor 1066, anda second terminal coupled to the second ground GND2.

As shown in FIG. 1, the commutator 108 includes a third switch 1082, afourth switch 1084, a fifth switch 1086, a sixth switch 1088, and athird inductor 1090. The third switch 1082 has a first terminal coupledto the first terminal of the third capacitor 1068, a second terminal forreceiving the switch control signal SCS, and a third terminal. Thefourth switch 1084 has a first terminal coupled to the first terminal ofthe third capacitor 1068, a second terminal for receiving the inverseswitch control signal SCS, and a third terminal coupled to a secondterminal of the load 112. The fifth switch 1086 has a first terminalcoupled to the third terminal of the third switch 1082, a secondterminal for receiving the inverse switch control signal SCS, and athird terminal coupled to the second ground GND2. The sixth switch 1090has a first terminal coupled to the third terminal of the fourth switch1084, a second terminal for receiving the switch control signal SCS, anda third terminal coupled to the second ground GND2. The third inductor1090 has a first terminal coupled to the third terminal of the thirdswitch 1082, and a second terminal coupled to a first terminal of theload 112, wherein the second inductor 1090 is used for filtering highfrequency components of the second inductor sinusoidal current IL of thesecond inductor 1066.

In addition, as shown in FIG. 1, the inverter 100 further includes afiltering capacitor 114. The filtering capacitor 114 has a firstterminal coupled to the first terminal of the direct current powersupply 110, and a second terminal coupled to a second terminal of thedirect current power supply 110, wherein the filtering capacitor 114 isused for filtering high frequency current ripples flowing through thefirst inductor 1042, and stabilizing the direct current voltage VDCprovided by the direct current power supply 110.

As shown in FIG. 1, the controller 102 controls an enabling time of thefirst pulse width modulation control signal FPWM according to the directcurrent IDC and a maximum power point tracking algorithm, controls anenabling time of the second pulse width modulation control signal SPWMaccording to the second inductor sinusoidal current IL (corresponding tooutput power PAC, wherein the output power PAC is equal to a product ofthe alternating current IAC flowing through the load 112 and analternating current voltage VAC of the load 112), and generates theswitch control signal SCS and the inverse switch control signal SCSaccording to a frequency of the alternating current voltage VAC, whereinthe enabling time of the first pulse width modulation control signalFPWM is greater than the enabling time of the second pulse widthmodulation control signal SPWM.

Please refer to FIG. 2 to FIG. 5. FIG. 2 is a relationship diagramillustrating the first pulse width modulation control signal FPWM, thesecond pulse width modulation control signal SPWM, a first inductorcurrent IM flowing through the first inductor 1042, and the secondinductor sinusoidal current IL flowing through the second inductor 1066,FIG. 3 is a diagram illustrating the current source inverter 100 in amode I, FIG. 4 is a diagram illustrating the current source inverter 100in a mode II, and FIG. 5 is a diagram illustrating the current sourceinverter 100 in a mode III.

As shown in FIG. 2 and FIG. 3, in the mode I, because the controller 102enables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, the first switch 1044and the second switch 1062 are turned on. Therefore, the input power PDCof the direct current power supply 110 is stored in the first inductor1042, a part of power stored in the first capacitor 1054 of the bufferunit 105 is transmitted to the magnetizing inductor 1056 of the bufferunit 105 and the second inductor 1066 of the modulating unit 106, otherpart of the power stored in the first capacitor 1054 of the buffer unit105 is transmitted to the commutator 108 through the modulating unit106, a part of power stored in the second capacitor 1058 of the bufferunit 105 is transmitted to the second inductor 1066 of the modulatingunit 106, and other part of the power stored in the second capacitor1058 of the buffer unit 105 is transmitted to the commutator 108 throughthe modulating unit 106. Meanwhile, the first capacitor 1054 of thebuffer unit 105 charges the magnetizing inductor 1056 of the buffer unit105. Therefore, the part of the power stored in the first capacitor 1054is stored in the second inductor 1066 and the magnetizing inductor 1056,and the other part of the power stored in the first capacitor 1054 istransmitted to the commutator 108 through the second inductor sinusoidalcurrent IL of the modulating unit 106. The part of the power stored inthe second capacitor 1058 is stored in the second inductor 1066, and theother part of the power stored in the second capacitor 1058 istransmitted to the commutator 108 through the second inductor sinusoidalcurrent IL of the modulating unit 106. Because the input power PDC ofthe direct current power supply 110 is stored in the first inductor1042, the first inductor current IM flowing through the first inductor1042 is increased (as shown in FIG. 2). In addition, because the part ofthe power stored in the first capacitor 1054 is stored in the secondinductor 1066 and the part of the power stored in the second capacitor1058 is stored in the second inductor 1066, the second inductorsinusoidal current IL flowing through the second inductor 1066 is alsoincreased (as shown in FIG. 2). In addition, in the model, thecontroller 102 can determine a turning-on time of the first switch 1044(that is, the enabling time of the first pulse width modulation controlsignal FPWM) according to the direct current IDC and the maximum powerpoint tracking algorithm, and the controller 102 can control aturning-on time of the second switch 1062 according to the secondinductor sinusoidal current IL.

As shown in FIG. 2 and FIG. 4, in the mode II, when the output power PACof the load 112 is satisfied, the controller 102 enables the first pulsewidth modulation control signal FPWM and disables the second pulse widthmodulation control signal SPWM, so the first switch 1044 is turned onand the second switch 1062 is turned off. Therefore, when the secondswitch 1062 is turned off, the alternating current IAC is generated bythe first diode 1064, the third capacitor 1068, and the second inductor1066, so power stored in the second inductor 1066 can be transmitted tothe commutator 108 through the second inductor sinusoidal current IL.But, because the direct current IDC is not yet increased to a directcurrent corresponding to a maximum power point of the direct currentpower supply 110, the first switch 1044 is continuously turned on,resulting in the input power PDC of the direct current power supply 110being continuously stored in the first inductor 1042, and the powerstored in the first capacitor 1054 of the buffer unit 105 beingtransmitted to the magnetizing inductor 1056 of the buffer unit 105through the first switch 1044 (that is, the first capacitor 1054 of thebuffer unit 105 continuously keeps charging the magnetizing inductor1056 of the buffer unit 105). Because the input power PDC of the directcurrent power supply 110 is continuously stored in the first inductor1042, the first inductor current IM flowing through the first inductor1042 is continuously increased (as shown in FIG. 2). In addition,because the power stored in the second inductor 1066 is transmitted tothe commutator 108, the second inductor sinusoidal current IL flowingthrough the second inductor 1066 is decreased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 5, in the mode III, when the direct currentIDC is increased to the direct current corresponding to the maximumpower point of the direct current power supply 110, the controller 102disables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, so the first switch1044 and the second switch 1062 are turned off. Therefore, when thesecond switch 1062 is turned off, the alternating current IAC isgenerated by the first diode 1064, the third capacitor 1068, and thesecond inductor 1066, so the power stored in the second inductor 1066can be transmitted to the commutator 108. Because the first switch 1044is turned off, power stored in the first inductor 1042 is stored in thefirst capacitor 1054 and stored in the second capacitor 1058 through thetransformer 1052, the parasitic diode 10622 of the second switch 1062,and the first diode 1064. In addition, the power stored in themagnetizing inductor 1056 can also be stored in the second capacitor1058 through the transformer 1052, the parasitic diode 10622 of thesecond switch 1062, and the first diode 1064. Because the power storedin the first inductor 1042 is stored in the first capacitor 1054 andstored in the second capacitor 1058 through the transformer 1052, theparasitic diode 10622 of the second switch 1062, and the first diode1064, the first inductor current IM flowing through the first inductor1042 is decreased (as shown in FIG. 2). Because the power stored in thesecond inductor 1066 is transmitted to the commutator 108, the secondinductor sinusoidal current IL flowing through the second inductor 1066is decreased (as shown in FIG. 2).

According to the mode I, the mode II, and the mode III of the currentsource inverter 100, because the controller 102 can control turning-onand turning-off of the first switch 1044 and the second switch 1062through the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, low frequency currentripples inversely generated by sinusoidal power outputted by themodulating unit 106 can be absorbed by the buffer unit 105, resulting inlow frequency current ripple components of the input power PDC beingdecreased.

Please refer to FIG. 6. FIG. 6 is a diagram illustrating a currentsource inverter 600 (isolation type) according to another embodiment. Asshown in FIG. 6, a difference between the current source inverter 600and the current source inverter 100 is that a buffer unit 605 and amodulating unit 606 of the current source inverter 600 are differentfrom the buffer unit 105 and the modulating unit 606 of the currentsource inverter 100. As shown in FIG. 6, the buffer unit 605 includes atransformer 6052, a first capacitor 1054, a magnetizing inductor 1056, asecond capacitor 1058, and a first diode 6060. The first capacitor 1054has a first terminal coupled to the second terminal of the firstinductor 1042, and a second terminal coupled to transformer 6052. Themagnetizing inductor 1056 has a first terminal coupled to the secondterminal of the first capacitor 1054 and the transformer 6052, and asecond terminal coupled to the first ground GND1 and the transformer6052. The second capacitor 1058 has a first terminal coupled to thetransformer 6052, and a second terminal coupled to the modulating unit606. The first diode 6060 has a first terminal coupled to the secondterminal of the second capacitor 1058, and a second terminal coupled tothe second ground GND2.

As shown in FIG. 6, the modulating unit 606 includes a second switch1062, a second diode 6064, a second inductor 6066, and a third capacitor1068. The second switch 1062 has a first terminal coupled to the secondterminal of the second capacitor 1058, a second terminal for receivingthe second pulse width modulation control signal SPWM, and a thirdterminal, wherein the second switch 1062 is turned on and turned offaccording to the second pulse width modulation control signal SPWM. Thesecond diode 6064 has a first terminal coupled to the third terminal ofthe second switch 1062, and a second terminal. The second inductor 6066has a first terminal coupled to the third terminal of the second switch1062, and a second terminal coupled to the second the ground GND2. Thethird capacitor 1068 has a first terminal coupled to the second terminalof the second diode 6064, and a second terminal coupled to the secondground GND2.

Please refer to FIG. 7 to FIG. 9. FIG. 7 is a diagram illustrating thecurrent source inverter 600 in a mode I, FIG. 8 is a diagramillustrating the current source inverter 600 in a mode II, and FIG. 9 isa diagram illustrating the current source inverter 600 in a mode III.

As shown in FIG. 2 and FIG. 7, in the mode I, because the controller 102enables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, the first switch 1044and the second switch 1062 are turned on. Therefore, the input power PDCof the direct current power supply 110 is stored in the first inductor1042, a part of power stored in the first capacitor 1054 of the bufferunit 605 is transmitted to the magnetizing inductor 1056 of the bufferunit 605 and the second inductor 6066 of the modulating unit 606, otherpart of the power stored in the first capacitor 1054 of the buffer unit605 is transmitted to the commutator 108 through the modulating unit606, apart of power stored in the second capacitor 1058 of the bufferunit 605 is transmitted to the second inductor 6066 of the modulatingunit 606, and other part of the power stored in the second capacitor1058 of the buffer unit 605 is transmitted to the commutator 108 throughthe modulating unit 606. Meanwhile, the first capacitor 1054 of thebuffer unit 605 charges the magnetizing inductor 1056 of the buffer unit605. Therefore, the part of the power stored in the first capacitor 1054is stored in the second inductor 6066 and the magnetizing inductor 1056,and the other part of the power stored in the first capacitor 1054 istransmitted to the commutator 108 through a second inductor sinusoidalcurrent IL of the modulating unit 606. The part of the power stored inthe second capacitor 1058 is stored in the second inductor 6066, and theother part of the power stored in the second capacitor 1058 istransmitted to the commutator 108 through the second inductor sinusoidalcurrent IL of the modulating unit 606. Because the input power PDC ofthe direct current power supply 110 is stored in the first inductor1042, the first inductor current IM flowing through the first inductor1042 is increased (as shown in FIG. 2). In addition, because the part ofthe power stored in the first capacitor 1054 is stored in the secondinductor 6066 and the part of the power stored in the second capacitor1058 is stored in the second inductor 6066, the second inductorsinusoidal current IL flowing through the second inductor 1066 is alsoincreased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 8, in the mode II, when the output power PACof the load 112 is satisfied, the controller 102 enables the first pulsewidth modulation control signal FPWM and disables the second pulse widthmodulation control signal SPWM, so the first switch 1044 is turned onand the second switch 1062 is turned off. Therefore, when the secondswitch 1062 is turned off, the alternating current IAC is generated bythe second diode 6064, the third capacitor 1068, and the second inductor6066, so power stored in the second inductor 6066 can be transmitted tothe commutator 108. But, because the direct current IDC is not yetincreased to the direct current corresponding to the maximum power pointof the direct current power supply 110, the first switch 1044 iscontinuously turned on, resulting in the input power PDC of the directcurrent power supply 110 being continuously stored in the first inductor1042, and the power stored in the first capacitor 1054 of the bufferunit 105 being transmitted to the magnetizing inductor 1056 of thebuffer unit 605 through the first switch 1044 (that is, the firstcapacitor 1054 of the buffer unit 605 continuously keeps charging themagnetizing inductor 1056 of the buffer unit 605). Because the inputpower PDC of the direct current power supply 110 is continuously storedin the first inductor 1042, the first inductor current IM flowingthrough the first inductor 1042 is continuously increased (as shown inFIG. 2). In addition, because the power stored in the second inductor6066 is transmitted to the commutator 108, the second inductorsinusoidal current IL flowing through the second inductor 6066 isdecreased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 9, in the mode III, when the direct currentIDC is increased to the direct current corresponding to the maximumpower point of the direct current power supply 110, the controller 102disables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, so the first switch1044 and the second switch 1062 are turned off. Therefore, when thesecond switch 1062 is turned off, the alternating current IAC isgenerated by the second diode 6064, the third capacitor 1068, and thesecond inductor 6066, so the power stored in the second inductor 6066can be transmitted to the commutator 108. Because the first switch 1044is turned off, the power stored in the first inductor 1042 is stored inthe first capacitor 1054 and stored in the second capacitor 1058 throughthe transformer 6052 and the first diode 6060. In addition, the powerstored in the magnetizing inductor 1056 can also be stored in the secondcapacitor 1058 through the transformer 6052 and the first diode 6060.Because the power stored in the first inductor 1042 is stored in thefirst capacitor 1054 and stored in the second capacitor 1058 through thetransformer 6052 and the first diode 6060, the first inductor current IMflowing through the first inductor 1042 is decreased (as shown in FIG.2); and because the power stored in the second inductor 6066 istransmitted to the commutator 108, the second inductor sinusoidalcurrent IL flowing through the second inductor 6066 is decreased (asshown in FIG. 2).

According to the mode I, the mode II, and the mode III of the currentsource inverter 600, because the controller 102 can control turning-onand turning-off of the first switch 1044 and the second switch 1062through the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, low frequency currentripples inversely generated by sinusoidal power outputted by themodulating unit 606 can be absorbed by the buffer unit 605, resulting inlow frequency current ripple components of the input power PDC beingdecreased.

Please refer to FIG. 10. FIG. 10 is a diagram illustrating a currentsource inverter 1000 (non-isolation type) according to anotherembodiment. As shown in FIG. 10, a difference between the current sourceinverter 1000 and the current source inverter 100 is that a buffer unit1005 of the current source inverter 1000 is different from the bufferunit 105 of the current source inverter 100. As shown in FIG. 10, thebuffer unit 1005 includes a first capacitor 10054. The first capacitor10054 has a first terminal coupled to the second terminal of the firstinductor 1042, and a second terminal coupled to the modulating unit 106.

Please refer to FIG. 11 to FIG. 13. FIG. 11 is a diagram illustratingthe current source inverter 1000 in a mode I, FIG. 12 is a diagramillustrating the current source inverter 1000 in a mode II, and FIG. 13is a diagram illustrating the current source inverter 1000 in a modeIII.

As shown in FIG. 2 and FIG. 11, in the mode I, because the controller102 enables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, the first switch 1044and the second switch 1062 are turned on. Therefore, the input power PDCof the direct current power supply 110 is stored in the first inductor1042, a part of power stored in the first capacitor 10054 of the bufferunit 1005 is transmitted to the second inductor 1066 of the modulatingunit 106, and other part of the power stored in the first capacitor10054 of the buffer unit 1005 is transmitted to the commutator 108through the second inductor sinusoidal current IL of the modulating unit106. Because the input power PDC of the direct current power supply 110is continuously stored in the first inductor 1042, the first inductorcurrent IM flowing through the first inductor 1042 is increased (asshown in FIG. 2). In addition, because the part of the power stored inthe first capacitor 10054 of the buffer unit 1005 is stored in thesecond inductor 1066 of the modulating unit 106, the second inductorsinusoidal current IL flowing through the second inductor 1066 is alsoincreased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 12, in the mode II, when the output powerPAC of the load 112 is satisfied, the controller 102 enables the firstpulse width modulation control signal FPWM and disables the second pulsewidth modulation control signal SPWM, so the first switch 1044 is turnedon and the second switch 1062 is turned off. Therefore, when the secondswitch 1062 is turned off, the alternating current IAC is generated bythe first diode 1064, third capacitor 1068, and the second inductor1066, so the power stored in the second inductor 1066 can be transmittedto the commutator 108. But, because the direct current IDC is not yetincreased to the direct current corresponding to the maximum power pointof the direct current power supply 110, the first switch 1044 iscontinuously turned on, resulting in the input power PDC of the directcurrent power supply 110 being continuously stored in the first inductor1042. Because the input power PDC of the direct current power supply 110is continuously stored in the first inductor 1042, the first inductorcurrent IM flowing through the first inductor 1042 is increasedcontinuously (as shown in FIG. 2). In addition, because the power storedin the second inductor 1066 is transmitted to the commutator 108, thesecond inductor sinusoidal current IL flowing through the secondinductor 1066 is decreased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 13, in the mode III, when the direct currentIDC is increased to the direct current corresponding to the maximumpower point of the direct current power supply 110, the controller 102disables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, so the first switch1044 and the second switch 1062 are turned off. Therefore, when thesecond switch 1062 is turned off, the alternating current IAC isgenerated by the first diode 1064, the third capacitor 1068, and thesecond inductor 1066, so the power stored in the second inductor 1066can be transmitted to the commutator 108. Because the first switch 1044is turned off, the power stored in the first inductor 1042 is stored inthe first capacitor 10054 through the parasitic diode 10622 of thesecond switch 1062 and the first diode 1064. Because the power stored inthe first inductor 1042 is stored in the first capacitor 10054, thefirst inductor current IM flowing through the first inductor 1042 isdecreased (as shown in FIG. 2); and because the power stored in thesecond inductor 1066 is transmitted to the commutator 108, the secondinductor sinusoidal current IL flowing through the second inductor 1066is decreased (as shown in FIG. 2).

According to the mode I, the mode II, and the mode III of the currentsource inverter 1000, because the controller 102 can control turning-onand turning-off of the first switch 1044 and the second switch 1062through the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, low frequency currentripples inversely generated by sinusoidal power outputted by themodulating unit 106 can be absorbed by the buffer unit 1005, resultingin low frequency current ripple components of the input power PDC beingdecreased.

Please refer to FIG. 14. FIG. 14 is a diagram illustrating a currentsource inverter 1400 (non-isolation type) according to anotherembodiment. As shown in FIG. 14, a difference between the current sourceinverter 1400 and the current source inverter 600 is that a buffer unit1405 of the current source inverter 1400 is different from the bufferunit 605 of the current source inverter 600. As shown in FIG. 14, thebuffer unit 1405 includes a first capacitor 14054 and a first diode14060. The first capacitor 14054 has a first terminal coupled to thesecond terminal of the first inductor 1042, and a second terminal; andthe first diode 14060 has a first terminal coupled to the secondterminal of the first capacitor 14054, and a second terminal coupled tothe ground GND1.

Please refer to FIG. 15 to FIG. 17. FIG. 15 is a diagram illustratingthe current source inverter 1400 in a mode I, FIG. 16 is a diagramillustrating the current source inverter 1400 in a mode II, and FIG. 17is a diagram illustrating the current source inverter 1400 in a modeIII.

As shown in FIG. 2 and FIG. 15, in the mode I, because the controller102 enables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, the first switch 1044and the second switch 1062 are turned on. Therefore, the input power PDCof the direct current power supply 110 is stored in the first inductor1042, a part of power stored in the first capacitor 14054 of the bufferunit 1405 is transmitted to the second inductor 6066 of the modulatingunit 606, and other part of the power stored in the first capacitor14054 of the buffer unit 1405 is transmitted to the commutator 108through the second inductor sinusoidal current IL of the modulating unit606. Therefore, the part of the power stored in the first capacitor14054 is stored in the second inductor 6066, and the other part of thepower stored in the first capacitor 14054 is transmitted to thecommutator 108 through the second inductor sinusoidal current IL of themodulating unit 606. Because the input power PDC of the direct currentpower supply 110 is continuously stored in the first inductor 1042, thefirst inductor current IM flowing through the first inductor 1042 isincreased (as shown in FIG. 2). In addition, because the part of thepower stored in the first capacitor 14054 is stored in the secondinductor 6066, the second inductor sinusoidal current IL flowing throughthe second inductor 6066 is also increased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 16, in the mode II, when the output powerPAC of the load 112 is satisfied, the controller 102 enables the firstpulse width modulation control signal FPWM and disables the second pulsewidth modulation control signal SPWM, so the first switch 1044 is turnedon and the second switch 1062 is turned off. Therefore, when the secondswitch 1062 is turned off, the alternating current IAC is generated bythe second diode 6064, the third capacitor 1068, and the second inductor6066, so the power stored in the second inductor 6066 can be transmittedto the commutator 108. But, because the direct current IDC is not yetincreased to the direct current corresponding to the maximum power pointof the direct current power supply 110, the first switch 1044 iscontinuously turned on, resulting in the input power PDC of the directcurrent power supply 110 being continuously stored in the first inductor1042. Because the input power PDC of the direct current power supply 110is continuously stored in the first inductor 1042, the first inductorcurrent IM flowing through the first inductor 1042 is continuouslyincreased (as shown in FIG. 2). In addition, because the power stored inthe second inductor 6066 is transmitted to the commutator 108, thesecond inductor sinusoidal current IL flowing through the secondinductor 6066 is decreased (as shown in FIG. 2).

As shown in FIG. 2 and FIG. 17, in the mode III, when the direct currentIDC is increased to the direct current corresponding to the maximumpower point of the direct current power supply 110, the controller 102disables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, so the first switch1044 and the second switch 1062 are turned off. Therefore, when thesecond switch 1062 is turned off, the alternating current IAC isgenerated by the second diode 6064, the third capacitor 1068, and thesecond inductor 6066, so the power stored in the second inductor 6066can be transmitted to the commutator 108. Because the first switch 1044is turned off, the power stored in the first inductor 1042 is stored inthe first capacitor 14054 through the first diode 14060. Because thepower stored in the first inductor 1042 is stored in the first capacitor14054 through the first diode 14060, the first inductor current IMflowing through the first inductor 1042 is decreased (as shown in FIG.2); and because the power stored in the second inductor 6066 istransmitted to the commutator 108, the second inductor sinusoidalcurrent IL flowing through the second inductor 6066 is decreased (asshown in FIG. 2).

According to the mode I, the mode II, and the mode III of the currentsource inverter 1400, because the controller 102 can control turning-onand turning-off of the first switch 1044 and the second switch 1062through the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, low frequency currentripples inversely generated by sinusoidal power outputted by themodulating unit 606 can be absorbed by the buffer unit 1405, resultingin low frequency current ripple components of the input power PDC beingdecreased.

Please refer to FIG. 1 to FIG. 5 and FIG. 18. FIG. 18 is a flowchartillustrating an operation method of a current source inverter accordingto another embodiment. The method in FIG. 18 is illustrated using thecurrent source inverter 100 in FIG. 1. Detailed steps are as follows:

Step 1800: Start.

Step 1802: The controller 102 generates a first pulse width modulationcontrol signal FPWM, a second pulse width modulation control signalSPWM, a switch control signal SCS, and an inverse switch control signalSCS.

Step 1804: When the first pulse width modulation control signal FPWM andthe second pulse width modulation control signal SPWM are enabled, go toStep 1806; when the first pulse width modulation control signal FPWM isenabled and the second pulse width modulation control signal SPWM isdisabled, go to Step 1808; and when the first pulse width modulationcontrol signal FPWM and the second pulse width modulation control signalSPWM are disabled, go to Step 1810.

Step 1806: The first inductor 1042 stores input power PDC of the directcurrent power supply 110, a part of power stored in the first capacitor1054 is stored in the second inductor 1066 and the magnetizing inductor1056, apart of the power stored in the second capacitor 1058 is storedin the second inductor 1066, and other part of the power stored in thefirst capacitor 1054 and other part of the power stored in the secondcapacitor 1058 are transmitted to the commutator 108 through themodulating unit 106, go to Step 1804.

Step 1808: The first inductor 1042 stores the input power PDC of thedirect current power supply 110, the part of the power stored in thefirst capacitor 1054 is transmitted to the magnetizing inductor 1056,and power stored in the second inductor 1066 is transmitted to thecommutator 108, go to Step 1804.

Step 1810: Power stored in the magnetizing inductor 1056 is stored inthe second capacitor 1058 through the transformer 1052, the parasiticdiode 10622 of the second switch 1062, and the first diode 1064, powerstored in the first inductor 1042 is stored in the first capacitor 1054and stored in the second capacitor 1058 through the transformer 1052,the parasitic diode 10622 of the second switch 1062, and the first diode1064, and the power stored in the second inductor 1066 is transmitted tothe commutator 108, go to Step 1804.

In Step 1802, as shown in FIG. 1, the controller 102 controls theenabling time of the first pulse width modulation control signal FPWMaccording to the direct current IDC and the maximum power point trackingalgorithm, controls the enabling time of the second pulse widthmodulation control signal SPWM according to the second inductorsinusoidal current IL (corresponding to the output power PAC), andgenerates the switch control signal SCS and the inverse switch controlsignal SCS according to the frequency of the alternating current voltageVAC, wherein the enabling time of the first pulse width modulationcontrol signal FPWM is greater than the enabling time of the secondpulse width modulation control signal SPWM.

In Step 1806, as shown in FIG. 2 and FIG. 3, because the controller 102enables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, the first switch 1044and the second switch 1062 are turned on. Therefore, the input power PDCof the direct current power supply 110 is stored in the first inductor1042, the part of the power stored in the first capacitor 1054 istransmitted to the magnetizing inductor 1056 and the second inductor1066, the other part of the power stored in the first capacitor 1054 istransmitted to the commutator 108 through the second inductor sinusoidalcurrent IL of the modulating unit 106, the part of the power stored inthe second capacitor 1058 is transmitted to the second inductor 1066,and the other part of the power stored in the second capacitor 1058 istransmitted to the commutator 108 through the second inductor sinusoidalcurrent IL of the modulating unit 106. Meanwhile, the first capacitor1054 of the buffer unit 105 charges the magnetizing inductor 1056 of thebuffer unit 105. Because the input power PDC of the direct current powersupply 110 is stored in the first inductor 1042, the first inductorcurrent IM flowing through the first inductor 1042 is increased (asshown in FIG. 2). In addition, because the part of the power stored inthe first capacitor 1054 is stored in the second inductor 1066 and thepart of the power stored in the second capacitor 1058 is stored in thesecond inductor 1066, the second inductor sinusoidal current IL flowingthrough the second inductor 1066 is also increased (as shown in FIG. 2).In addition, in the mode I, the controller 102 can determine theturning-on time of the first switch 1044 (that is, the enabling time ofthe first pulse width modulation control signal FPWM) according to thedirect current IDC and the maximum power point tracking algorithm, andthe controller 102 can control the turning-on time of the second switch1062 according to the second inductor sinusoidal current IL.

In Step 1808, as shown in FIG. 2 and FIG. 4, when the output power PACof the load 112 is satisfied, the controller 102 enables the first pulsewidth modulation control signal FPWM and disables the second pulse widthmodulation control signal SPWM, so the first switch 1044 is turned onand the second switch 1062 is turned off. Therefore, when the secondswitch 1062 is turned off, the alternating current IAC is generated bythe first diode 1064, the third capacitor 1068, and the second inductor1066, so the power stored in the second inductor 1066 can be transmittedto the commutator 108 through the second inductor sinusoidal current IL.But, because the direct current IDC is not yet increased to the directcurrent corresponding to the maximum power point of the direct currentpower supply 110, the first switch 1044 is continuously turned on,resulting in the input power PDC of the direct current power supply 110being continuously stored in the first inductor 1042, and the powerstored in the first capacitor 1054 of the buffer unit 105 beingtransmitted to the magnetizing inductor 1056 of the buffer unit 105through the first switch 1044 (that is, the first capacitor 1054 of thebuffer unit 105 continuously keeps charging the magnetizing inductor1056 of the buffer unit 105). Because the input power PDC of the directcurrent power supply 110 is continuously stored in the first inductor1042, the first inductor current IM flowing through the first inductor1042 is continuously increased (as shown in FIG. 2). In addition,because the power stored in the second inductor 1066 is transmitted tothe commutator 108, the second inductor sinusoidal current IL flowingthrough the second inductor 1066 is decreased (as shown in FIG. 2).

In Step 1810, as shown in FIG. 2 and FIG. 5, when direct current IDC isincreased to the direct current corresponding to the maximum power pointof the direct current power supply 110, the controller 102 disables thefirst pulse width modulation control signal FPWM and the second pulsewidth modulation control signal SPWM, so the first switch 1044 and thesecond switch 1062 are turned off. Therefore, when the second switch1062 is turned off, the alternating current IAC is generated by thefirst diode 1064, the third capacitor 1068, and the second inductor1066, so the power stored in the second inductor 1066 can be transmittedto the commutator 108. Because the first switch 1044 is turned off, thepower stored in the first inductor 1042 is stored in the first capacitor1054 and stored in the second capacitor 1058 through the transformer1052, the parasitic diode 10622 of the second switch 1062, and the firstdiode 1064. In addition, the power stored in the magnetizing inductor1056 can also be stored in the second capacitor 1058 through thetransformer 1052, the parasitic diode 10622 of the second switch 1062,and the first diode 1064. Because the power stored in the first inductor1042 is stored in the first capacitor 1054 and stored in the secondcapacitor 1058 through the transformer 1052, the parasitic diode 10622of the second switch 1062, and the first diode 1064, the first inductorcurrent IM flowing through the first inductor 1042 is decreased (asshown in FIG. 2); and because the power stored in the second inductor1066 is transmitted to the commutator 108, the second inductorsinusoidal current IL flowing through the second inductor 1066 isdecreased (as shown in FIG. 2).

Please refer to FIG. 2, FIG. 6 to FIG. 9, and FIG. 19. FIG. 19 is aflowchart illustrating an operation method of a current source inverteraccording to another embodiment. The method in FIG. 19 is illustratedusing the current source inverter 600 in FIG. 6. Detailed steps are asfollows:

Step 1900: Start.

Step 1902: The controller 102 generates a first pulse width modulationcontrol signal FPWM, a second pulse width modulation control signalSPWM, a switch control signal SCS, and an inverse switch control signalSCS.

Step 1904: When the first pulse width modulation control signal FPWM andthe second pulse width modulation control signal SPWM are enabled, go toStep 1906; when the first pulse width modulation control signal FPWM isenabled and the second pulse width modulation control signal SPWM isdisabled, go to Step 1908; and when the first pulse width modulationcontrol signal FPWM and the second pulse width modulation control signalSPWM are disabled, go to Step 1910.

Step 1906: The first inductor 1042 stores input power PDC of the directcurrent power supply 110, a part of power stored in the first capacitor1054 is stored in the second inductor 6066 and the magnetizing inductor1056, a part of power stored in the second capacitor 1058 is stored inthe second inductor 6066, and other part of the power stored in thefirst capacitor 1054 and other part of the power stored in the secondcapacitor 1058 are transmitted to the commutator 108 through themodulating unit 606, go to Step 1904.

Step 1908: The first inductor 1042 stores the input power PDC of thedirect current power supply 110, the part of the power stored in thefirst capacitor 1054 is transmitted to the magnetizing inductor 1056,and power stored in the second inductor 6066 is transmitted to thecommutator 108, go to Step 1904.

Step 1910: Power stored in the magnetizing inductor 1056 is stored inthe second capacitor 1058 through the transformer 6052 and the firstdiode 6060, power stored in the first inductor 1042 is stored in thefirst capacitor 1054 and stored in the second capacitor 1058 through thetransformer 6052 and the first diode 6060, and power stored in thesecond inductor 6066 is transmitted to the commutator 108, go to Step1904.

A difference between the embodiment in FIG. 19 and the embodiment inFIG. 18 is that in Step 1910, as shown in FIG. 2 and FIG. 9, when thedirect current IDC is increased to the direct current corresponding tothe maximum power point of the direct current power supply 110, thecontroller 102 disables the first pulse width modulation control signalFPWM and the second pulse width modulation control signal SPWM, so thefirst switch 1044 and the second switch 1062 are turned off. Therefore,when the second switch 1062 is turned off, the alternating current IACis generated by the second diode 6064, the third capacitor 1068, and thesecond inductor 6066, so the power stored in the second inductor 6066can be transmitted to the commutator 108. Because the first switch 1044is turned off, the power stored in the first inductor 1042 is stored inthe first capacitor 1054 and stored in the second capacitor 1058 throughthe transformer 6052 and the first diode 6060. In addition, the powerstored in the magnetizing inductor 1056 can also be stored in the secondcapacitor 1058 through the transformer 6052 and the first diode 6060. Inaddition, subsequent operational principles of the embodiment in FIG. 19are the same as those of the embodiment in FIG. 18, so furtherdescription thereof is omitted for simplicity.

Please refer to FIG. 2, FIG. 10 to FIG. 13, and FIG. 20. FIG. 20 is aflowchart illustrating an operation method of a current source inverteraccording to another embodiment. The method in FIG. 20 is illustratedusing the current source inverter 1000 in FIG. 10. Detailed steps are asfollows:

Step 2000: Start.

Step 2002: The controller 102 generates a first pulse width modulationcontrol signal FPWM, a second pulse width modulation control signalSPWM, a switch control signal SCS, and an inverse switch control signalSCS.

Step 2004: When the first pulse width modulation control signal FPWM andthe second pulse width modulation control signal SPWM are enabled, go toStep 2006; when the first pulse width modulation control signal FPWM isenabled and the second pulse width modulation control signal SPWM isdisabled, go to Step 2008; and when the first pulse width modulationcontrol signal FPWM and the second pulse width modulation control signalSPWM are disabled, go to Step 2010.

Step 2006: The first inductor 1042 stores input power PDC of the directcurrent power supply 110, a part of power stored in the first capacitor10054 is stored in the second inductor 1066, and other part of the powerstored in the first capacitor 10054 is transmitted to the commutator 108through the modulating unit 106, go to Step 2004.

Step 2008: The first inductor 1042 stores the input power PDC of thedirect current power supply 110, and power stored in the second inductor1066 is transmitted to the commutator 108, go to Step 2004.

Step 2010: Power stored in the first inductor 1042 is stored in thefirst capacitor 10054 through the parasitic diode 10622 of the secondswitch 1062 and the first diode 1064, and the power stored in the secondinductor 1066 is transmitted to the commutator 108, go to Step 2004.

In Step 2006, as shown in FIG. 2 and FIG. 11, because the controller 102enables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, the first switch 1044and the second switch 1062 are turned on. Therefore, the input power PDCof the direct current power supply 110 is stored in the first inductor1042, the part of the power stored in the first capacitor 10054 istransmitted to the second inductor 1066 of the modulating unit 106, andthe other part of the power stored in the first capacitor 10054 istransmitted to the commutator 108 through the second inductor sinusoidalcurrent IL of the modulating unit 106.

In Step 2008, as shown in FIG. 2 and FIG. 12, when the output power PACof the load 112 is satisfied, the controller 102 enables the first pulsewidth modulation control signal FPWM and disables the second pulse widthmodulation control signal SPWM, so the first switch 1044 is turned onand the second switch 1062 is turned off. Therefore, when the secondswitch 1062 is turned off, the alternating current IAC is generated bythe first diode 1064, the third capacitor 1068, and the second inductor1066, so the power stored in the second inductor 1066 can be transmittedto the commutator 108. But, because the direct current IDC is not yetincreased to the direct current corresponding to the maximum power pointof the direct current power supply 110, the first switch 1044 iscontinuously turned on, resulting in the input power PDC of the directcurrent power supply 110 being continuously stored in the first inductor1042.

In Step 2010, as shown in FIG. 2 and FIG. 13, when the direct currentIDC is increased to the direct current corresponding to the maximumpower point of the direct current power supply 110, the controller 102disables the first pulse width modulation control signal FPWM and thesecond pulse width modulation control signal SPWM, so the first switch1044 and the second switch 1062 are turned off. Therefore, when thesecond switch 1062 is turned off, the alternating current IAC isgenerated by the first diode 1064, the third capacitor 1068, and thesecond inductor 1066, so the power stored in the second inductor 1066can be transmitted to the commutator 108. Because the first switch 1044is turned off, the power stored in the first inductor 1042 is stored inthe first capacitor 10054 through the parasitic diode 10622 of thesecond switch 1062 and the first diode 1064.

Please refer to FIG. 2, FIG. 14 to FIG. 17, and FIG. 21. FIG. 21 is aflowchart illustrating an operation method of a current source inverteraccording to another embodiment. The method in FIG. 21 is illustratedusing the current source inverter 1400 in FIG. 14. Detailed steps are asfollows:

Step 2100: Start.

Step 2102: The controller 102 generates a first pulse width modulationcontrol signal FPWM, a second pulse width modulation control signalSPWM, a switch control signal SCS, and an inverse switch control signalSCS.

Step 2104: When the first pulse width modulation control signal FPWM andthe second pulse width modulation control signal SPWM are enabled, go toStep 2106; when the first pulse width modulation control signal FPWM isenabled and the second pulse width modulation control signal SPWM isdisabled, go to Step 2108; and when the first pulse width modulationcontrol signal FPWM and the second pulse width modulation control signalSPWM are disabled, go to Step 2110.

Step 2106: The first inductor 1042 stores input power PDC of the directcurrent power supply 110, a part of power stored in the first capacitor14054 is stored in the second inductor 6066, and other part of the powerstored in the first capacitor 14054 is transmitted to the commutator 108through the modulating unit 606, go to Step 2104.

Step 2108: The first inductor 1042 stores the input power PDC of thedirect current power supply 110, and power stored in the second inductor6066 is transmitted to the commutator 108, go to Step 2104.

Step 2110: Power stored in the first inductor 1042 is stored in thefirst capacitor 14054 through the first diode 14060, and the powerstored in the second inductor 6066 is transmitted to the commutator 108,go to Step 2104.

A difference between the embodiment in FIG. 21 and the embodiment inFIG. 20 is that in Step 2110, as shown in FIG. 2 and FIG. 17, when thedirect current IDC is increased to the direct current corresponding tothe maximum power point of the direct current power supply 110, thecontroller 102 disables the first pulse width modulation control signalFPWM and the second pulse width modulation control signal SPWM, so thefirst switch 1044 and the second switch 1062 are turned off. Therefore,when the second switch 1062 is turned off, the alternating current IACis generated by the second diode 6064, the third capacitor 1068, and thesecond inductor 6066, so the power stored in the second inductor 6066can be transmitted to the commutator 108. Because the first switch 1044is turned off, the power stored in the first inductor 1042 is stored inthe first capacitor 14054 through the first diode 14060. In addition,subsequent operational principles of the embodiment in FIG. 21 are thesame as those of the embodiment in FIG. 20, so further descriptionthereof is omitted for simplicity.

To sum up, the current source inverter and the operation method thereofutilize the input unit to execute a first corresponding operationaccording to a first pulse width modulation control signal, themodulating unit to execute a second corresponding operation according toa second pulse width modulation control signal, and the buffer unit toexecute a third corresponding operation according to the second pulsewidth modulation control signal. Therefore, compared to the prior art,the present invention has advantages as follows: first, because thecontroller can control turning-on and turning-off of the first switchand the second switch through the first pulse width modulation controlsignal and the second pulse width modulation control signal, lowfrequency current ripples inversely generated by sinusoidal poweroutputted by the modulating unit modulating unit can be absorbed by thebuffer unit, resulting in low frequency current ripple components ofinput power being decreased, to increase power conversion efficiency ofthe current source inverter; second, when the current source inverter(isolation type) operates, because a voltage drop of the first capacitoris connected to a voltage drop of the second capacitor in series, thevoltage drop of the second capacitor does not need to be higher than avoltage drop of the load, resulting in the second switch easilytransmitting power to the load and not enduring stress corresponding tolonger turning-on time, and operation range of the direct current powersupply being also very large; third, because the first inductor and thesecond inductor of the current source inverter operate in a continuouscurrent mode (CCM), current stress on the first switch and the secondswitch is not very large; and fourth, the second switches of the currentsource inverters shown in FIGS. 1, 10 can be still turned on throughparasitic diodes thereof during a mode III, so the second switches ofthe current source inverters shown in FIGS. 1, 10 have a zero voltageswitching characteristic when the second switches of the current sourceinverters shown in FIGS. 1, 10 are switched from the mode III to a modeI, resulting in switching loss of the second switches of the currentsource inverters shown in FIGS. 1, 10 being decreased.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A current source inverter, comprising: acontroller for generating a switch control signal, an inverse switchcontrol signal, a first pulse width modulation control signal, and asecond pulse width modulation control signal; an input unit coupled to adirect current power supply, and for storing and transmitting inputpower of the direct current power supply according to the first pulsewidth modulation control signal; a buffer unit coupled to the input unitfor receiving and transmitting the input power, wherein the buffer unitcomprises: a transformer; a first capacitor having a first terminalcoupled to the input unit, and a second terminal coupled to thetransformer; a magnetizing inductor having a first terminal coupled tothe second terminal of the first capacitor and the transformer, and asecond terminal coupled to first ground and the transformer; and asecond capacitor having a first terminal coupled to the transformer, anda second terminal coupled to the modulating unit; a modulating unitcoupled to the buffer unit for receiving the input power according tothe second pulse width modulation control signal, and generating andoutputting a full-wave rectified sinusoidal current according to theinput power; and a commutator coupled to the modulating unit forconverting the full-wave rectified sinusoidal current into analternating current according to the switch control signal and theinverse switch control signal, and outputting the alternating current toa load, wherein a frequency of the switch control signal and a frequencyof the inverse switch control signal are equal to a frequency of theload; wherein the controller controls an enabling time of the secondpulse width modulation control signal according to the sinusoidalcurrent, and an enabling time of the first pulse width modulationcontrol signal is greater than the enabling time of the second pulsewidth modulation control signal.
 2. The current source inverter of claim1, further comprising: a filtering capacitor having a first terminalcoupled to a first terminal of the direct current power supply, and asecond terminal coupled to a second terminal of the direct current powersupply and first ground, wherein the filtering capacitor is used forfiltering high frequency current ripples of a direct current voltageprovided by the direct current power supply.
 3. The current sourceinverter of claim 2, wherein the input power is equal to a product ofthe direct current voltage and a direct current provided by the directcurrent power supply, wherein the direct current corresponds to themaximum power point tracking, and the controller controls the enablingtime of the first pulse width modulation control signal according to thedirect current and a maximum power point tracking algorithm.
 4. Thecurrent source inverter of claim 1, wherein output power of the load isequal to a product of the alternating current and a voltage of the load.5. The current source inverter of claim 1, wherein the direct currentpower supply is a solar panel or a stable direct current power supply.6. The current source inverter of claim 5, wherein the input unit has amaximum power point tracking function.
 7. The current source inverter ofclaim 6, wherein the input unit comprises: a first inductor having afirst terminal coupled to a first terminal of the direct current powersupply, and a second terminal; and a first switch having a firstterminal coupled to the second terminal of the first inductor, a secondterminal for receiving the first pulse width modulation control signal,and a third terminal coupled to first ground, wherein the first switchis turned on and turned off according to the first pulse widthmodulation control signal.
 8. The current source inverter of claim 1,wherein the modulating unit comprises: a second switch having a firstterminal coupled to the second terminal of the second capacitor, asecond terminal for receiving the second pulse width modulation controlsignal, and a third terminal, wherein the second switch is turned on andturned off according to the second pulse width modulation controlsignal; a first diode having a first terminal coupled to second ground,and a second terminal coupled to the third terminal of the secondswitch; a second inductor having a first terminal coupled to the secondterminal of the first diode, and a second terminal; and a thirdcapacitor having a first terminal coupled to the second terminal of thesecond inductor, and a second terminal coupled to the second ground. 9.The current source inverter of claim 8, wherein the commutatorcomprises: a third switch having a first terminal coupled to the firstterminal of the third capacitor, a second terminal for receiving theswitch control signal, and a third terminal; a fourth switch having afirst terminal coupled to the first terminal of the third capacitor, asecond terminal for receiving the inverse switch control signal, and athird terminal coupled to a second terminal of the load; a fifth switchhaving a first terminal coupled to the third terminal of the thirdswitch, a second terminal for receiving the inverse switch controlsignal, and a third terminal coupled to the second ground; a sixthswitch having a first terminal coupled to the third terminal of thefourth switch, a second terminal for receiving the switch controlsignal, and a third terminal coupled to the second ground; and a thirdinductor having a first terminal coupled to the third terminal of thethird switch, and a second terminal coupled to a first terminal of theload.
 10. The current source inverter of claim 9, wherein when a firstswitch of the input unit and the second switch are turned on, the inputpower is stored in a first inductor of the input unit; a part of powerstored in the first capacitor is stored in the second inductor and themagnetizing inductor, and other part of the power stored in the firstcapacitor is transmitted to the commutator through the modulating unit;a part of power stored in the second capacitor is stored in the secondinductor, and other part of the power stored in the second capacitor istransmitted to the commutator through the modulating unit.
 11. Thecurrent source inverter of claim 9, wherein when the second switch isturned off and a first switch of the input unit is turned on, the inputpower is stored in a first inductor of the input unit, power stored inthe first capacitor is transmitted to the magnetizing inductor throughthe first switch, and power stored in the second inductor is transmittedto the commutator.
 12. The current source inverter of claim 9, whereinwhen a first switch of the input unit and the second switch are turnedoff, power stored in the magnetizing inductor is stored in the secondcapacitor through the transformer, a parasitic diode of the secondswitch, and the first diode, power stored in a first inductor of theinput unit is stored in the first capacitor, and stored in the secondcapacitor through the transformer, the parasitic diode of the secondswitch, and the first diode, and power stored in the second inductor istransmitted to the commutator.
 13. The current source inverter of claim9, wherein when a first switch of the input unit and the second switchare turned off, power stored in the magnetizing inductor is stored inthe second capacitor through the transformer and the first diode, powerstored in a first inductor of the input unit is stored in the firstcapacitor, and stored in the second capacitor through the transformerand the first diode, and power stored in the second inductor istransmitted to the commutator.
 14. A current source inverter,comprising: a controller for generating a switch control signal, aninverse switch control signal, a first pulse width modulation controlsignal, and a second pulse width modulation control signal; an inputunit coupled to a direct current power supply, and for storing andtransmitting input power of the direct current power supply according tothe first pulse width modulation control signal; a buffer unit coupledto the input unit for receiving and transmitting the input power,wherein the buffer unit comprises: a transformer; a first capacitorhaving a first terminal coupled to the input unit, and a second terminalcoupled to the transformer; a magnetizing inductor having a firstterminal coupled to the second terminal of the first capacitor and thetransformer, and a second terminal coupled to first ground and thetransformer; and a second capacitor having a first terminal coupled tothe transformer, and a second terminal coupled to the modulating unit;and a first diode having a first terminal coupled to the second terminalof the second capacitor, and a second terminal coupled to second ground;a modulating unit coupled to the buffer unit for receiving the inputpower according to the second pulse width modulation control signal, andgenerating and outputting a full-wave rectified sinusoidal currentaccording to the input power; and a commutator coupled to the modulatingunit for converting the full-wave rectified sinusoidal current into analternating current according to the switch control signal and theinverse switch control signal, and outputting the alternating current toa load, wherein a frequency of the switch control signal and a frequencyof the inverse switch control signal are equal to a frequency of theload; wherein the controller controls an enabling time of the secondpulse width modulation control signal according to the sinusoidalcurrent, and an enabling time of the first pulse width modulationcontrol signal is greater than the enabling time of the second pulsewidth modulation control signal.
 15. The current source inverter ofclaim 14, wherein the modulating unit comprises: a second switch havinga first terminal coupled to the second terminal of the second capacitor,a second terminal for receiving the second pulse width modulationcontrol signal, and a third terminal, wherein the second switch isturned on and turned off according to the second pulse width modulationcontrol signal; a second inductor having a first terminal coupled to thethird terminal of the second switch, and a second terminal coupled tothe second ground; a second diode having a first terminal coupled to thethird terminal of the second switch, and a second terminal; and a thirdcapacitor having a first terminal coupled to the second terminal of thesecond diode, and a second terminal coupled to the second ground. 16.The current source inverter of claim 15, wherein the commutatorcomprises: a third switch having a first terminal coupled to the firstterminal of the third capacitor, a second terminal for receiving theswitch control signal, and a third terminal; a fourth switch having afirst terminal coupled to the first terminal of the third capacitor, asecond terminal for receiving the inverse switch control signal, and athird terminal coupled to a second terminal of the load; a fifth switchhaving a first terminal coupled to the third terminal of the thirdswitch, a second terminal for receiving the inverse switch controlsignal, and a third terminal coupled to the second ground; a sixthswitch having a first terminal coupled to the third terminal of thefourth switch, a second terminal for receiving the switch controlsignal, and a third terminal coupled to the second ground; and a thirdinductor having a first terminal coupled to the third terminal of thethird switch, and a second terminal coupled to a first terminal of theload.
 17. The current source inverter of claim 16, wherein when a firstswitch of the input unit and the second switch are turned on, the inputpower is stored in a first inductor of the input unit; a part of powerstored in the first capacitor is stored in the second inductor and themagnetizing inductor, and other part of the power stored in the firstcapacitor is transmitted to the commutator through the modulating unit;a part of power stored in the second capacitor is stored in the secondinductor, and other part of the power stored in the second capacitor istransmitted to the commutator through the modulating unit.
 18. Thecurrent source inverter of claim 16, wherein when the second switch isturned off and a first switch of the input unit is turned on, the inputpower is stored in a first inductor of the input unit, power stored inthe first capacitor is transmitted to the magnetizing inductor throughthe first switch, and power stored in the second inductor is transmittedto the commutator.
 19. The current source inverter of claim 16, whereinwhen a first switch of the input unit and the second switch are turnedoff, power stored in the magnetizing inductor is stored in the secondcapacitor through the transformer, a parasitic diode of the secondswitch, and the first diode, power stored in a first inductor of theinput unit is stored in the first capacitor, and stored in the secondcapacitor through the transformer, the parasitic diode of the secondswitch, and the first diode, and power stored in the second inductor istransmitted to the commutator.
 20. The current source inverter of claim16, wherein when a first switch of the input unit and the second switchare turned off, power stored in the magnetizing inductor is stored inthe second capacitor through the transformer and the first diode, powerstored in a first inductor of the input unit is stored in the firstcapacitor, and stored in the second capacitor through the transformerand the first diode, and power stored in the second inductor istransmitted to the commutator.
 21. A current source inverter,comprising: a controller for generating a switch control signal, aninverse switch control signal, a first pulse width modulation controlsignal, and a second pulse width modulation control signal; an inputunit coupled to a direct current power supply, and for storing andtransmitting input power of the direct current power supply according tothe first pulse width modulation control signal; a buffer unit coupledto the input unit for receiving and transmitting the input power,wherein the buffer unit comprises: a first capacitor having a firstterminal coupled to the input unit, and a second terminal coupled to themodulating unit; a modulating unit coupled to the buffer unit forreceiving the input power according to the second pulse width modulationcontrol signal, and generating and outputting a full-wave rectifiedsinusoidal current according to the input power, wherein the modulatingunit comprises: a second switch having a first terminal coupled to thesecond terminal of the first capacitor, a second terminal for receivingthe second pulse width modulation control signal, and a third terminal,wherein the second switch is turned on and turned off according to thesecond pulse width modulation control signal; a first diode having afirst terminal coupled to the third terminal of the second switch, and asecond terminal coupled to first ground; a second inductor having afirst terminal coupled to the first terminal of the first diode, and asecond terminal; and a second capacitor having a first terminal coupledto the second terminal of the second inductor, and a second terminalcoupled to the first ground; and a commutator coupled to the modulatingunit for converting the full-wave rectified sinusoidal current into analternating current according to the switch control signal and theinverse switch control signal, and outputting the alternating current toa load, wherein a frequency of the switch control signal and a frequencyof the inverse switch control signal are equal to a frequency of theload; wherein the controller controls an enabling time of the secondpulse width modulation control signal according to the sinusoidalcurrent, and an enabling time of the first pulse width modulationcontrol signal is greater than the enabling time of the second pulsewidth modulation control signal.
 22. The current source inverter ofclaim 21, wherein the commutator comprises: a third switch having afirst terminal coupled to the first terminal of the second capacitor, asecond terminal for receiving the switch control signal, and a thirdterminal; a fourth switch having a first terminal coupled to the firstterminal of the second capacitor, a second terminal for receiving theinverse switch control signal, and a third terminal coupled to a secondterminal of the load; a fifth switch having a first terminal coupled tothe third terminal of the third switch, a second terminal for receivingthe inverse switch control signal, and a third terminal coupled to thefirst ground; a sixth switch having a first terminal coupled to thethird terminal of the fourth switch, a second terminal for receiving theswitch control signal, and a third terminal coupled to the first ground;and a third inductor having a first terminal coupled to the thirdterminal of the third switch, and a second terminal coupled to a firstterminal of the load.
 23. The current source inverter of claim 22,wherein when a first switch of the input unit and the second switch areturned on, the input power is stored in a first inductor of the inputunit, a part of power stored in the first capacitor is stored in thesecond inductor, and other part of the power stored in the firstcapacitor is transmitted to the commutator through the modulating unit.24. The current source inverter of claim 22, wherein when the secondswitch is turned off and a first switch of the input unit is turned on,the input power is stored in a first inductor of the input unit, andpower stored in the second inductor is transmitted to the commutator.25. The current source inverter of claim 22, wherein when a first switchof the input unit and the second switch are turned off, power stored ina first inductor of the input unit is stored in the first capacitorthrough a parasitic diode of the second switch and the first diode, andpower stored in the second inductor is transmitted to the commutator.26. The current source inverter of claim 22, wherein when a first switchof the input unit and the second switch are turned off, power stored ina first inductor of the input unit is stored in the first capacitorthrough the first diode, and power stored in the second inductor istransmitted to the commutator.
 27. A current source inverter,comprising: a controller for generating a switch control signal, aninverse switch control signal, a first pulse width modulation controlsignal, and a second pulse width modulation control signal; an inputunit coupled to a direct current power supply, and for storing andtransmitting input power of the direct current power supply according tothe first pulse width modulation control signal; a buffer unit coupledto the input unit for receiving and transmitting the input power,wherein the buffer unit comprises: a first capacitor having a firstterminal coupled to the input unit, and a second terminal; and a firstdiode having a first terminal coupled to the second terminal of thefirst capacitor, and a second terminal coupled to first ground; amodulating unit coupled to the buffer unit for receiving the input poweraccording to the second pulse width modulation control signal, andgenerating and outputting a full-wave rectified sinusoidal currentaccording to the input power, wherein the modulating unit comprises: asecond switch having a first terminal coupled to the second terminal ofthe first capacitor, a second terminal for receiving the second pulsewidth modulation control signal, and a third terminal, wherein thesecond switch is turned on and turned off according to the second pulsewidth modulation control signal; a second inductor having a firstterminal coupled to the third terminal of the second switch, and asecond terminal coupled to the first ground; a second diode having afirst terminal coupled to the third terminal of the second switch, and asecond terminal; and a second capacitor having a first terminal coupledto the second terminal of the second diode, and a second terminalcoupled to the first ground; and a commutator coupled to the modulatingunit for converting the full-wave rectified sinusoidal current into analternating current according to the switch control signal and theinverse switch control signal, and outputting the alternating current toa load, wherein a frequency of the switch control signal and a frequencyof the inverse switch control signal are equal to a frequency of theload; wherein the controller controls an enabling time of the secondpulse width modulation control signal according to the sinusoidalcurrent, and an enabling time of the first pulse width modulationcontrol signal is greater than the enabling time of the second pulsewidth modulation control signal.
 28. The current source inverter ofclaim 27, wherein the commutator comprises: a third switch having afirst terminal coupled to the first terminal of the second capacitor, asecond terminal for receiving the switch control signal, and a thirdterminal; a fourth switch having a first terminal coupled to the firstterminal of the second capacitor, a second terminal for receiving theinverse switch control signal, and a third terminal coupled to a secondterminal of the load; a fifth switch having a first terminal coupled tothe third terminal of the third switch, a second terminal for receivingthe inverse switch control signal, and a third terminal coupled to thefirst ground; a sixth switch having a first terminal coupled to thethird terminal of the fourth switch, a second terminal for receiving theswitch control signal, and a third terminal coupled to the first ground;and a third inductor having a first terminal coupled to the thirdterminal of the third switch, and a second terminal coupled to a firstterminal of the load.
 29. The current source inverter of claim 28,wherein when a first switch of the input unit and the second switch areturned on, the input power is stored in a first inductor of the inputunit, a part of power stored in the first capacitor is stored in thesecond inductor, and other part of the power stored in the firstcapacitor is transmitted to the commutator through the modulating unit.30. The current source inverter of claim 28, wherein when the secondswitch is turned off and a first switch of the input unit is turned on,the input power is stored in a first inductor of the input unit, andpower stored in the second inductor is transmitted to the commutator.31. The current source inverter of claim 28, wherein when a first switchof the input unit and the second switch are turned off, power stored ina first inductor of the input unit is stored in the first capacitorthrough a parasitic diode of the second switch and the first diode, andpower stored in the second inductor is transmitted to the commutator.32. The current source inverter of claim 28, wherein when a first switchof the input unit and the second switch are turned off, power stored ina first inductor of the input unit is stored in the first capacitorthrough the first diode, and power stored in the second inductor istransmitted to the commutator.